The present invention relates to a perpendicular magnetic recording medium and its manufacturing to which perpendicular magnetic recording technology is applied.
Perpendicular magnetic recording is attracting attention as a technology for enhancing areal recording density to make capacity of a magnetic recording medium large. The perpendicular magnetic recording is a system in which recorded bits are formed such that magnetization of the recording medium becomes normal to medium plane and magnetization in adjacent recorded bits becomes antiparallel to each other. Since the demagnetizing field is low in a magnetization transition region in the perpendicular magnetic recording system, a steep magnetization transition region is formed compared to longitudinal magnetic recording system, and the magnetization is stabilized at a high density. Accordingly, film thickness is allowed to be thicker, and thus the volume of magnetic crystal grains is allowed to be larger to acquire similar resolution compared with the longitudinal magnetic recording system, thereby enabling attenuation of recorded magnetization with time, i.e., thermal demagnetization, to be suppressed. Moreover, an intense magnetic recording field is obtained in a combination of a single pole type head and a perpendicular magnetic recording medium provided with a perpendicular magnetic recording layer and a soft-magnetic underlayer, allowing a material with high magnetic anisotropy to be selected for the perpendicular magnetic recording layer as well as thermal demagnetization to be further suppressed.
Currently, crystalline film of CoCr-based crystal alloy film is the mainstream of recording material for perpendicular magnetic recording medium. By controlling crystallographic orientation in a way that the c axis of CoCr crystal having an hcp structure becomes normal to medium plane, the axis of easy magnetization of the magnetic recording layer can be kept normal to medium plane. Here, the medium noises can be reduced and the recording density can be improved by making the grain size of CoCr-based crystal alloy small as well as its size variations reduced, and thus allowing magnetic exchange interactions among individual grains to be decreased. As a mode of controlling such a structure of the magnetic recording layer, a magnetic recording layer generally called granular thin film in which the periphery of ferromagnetic grains is surrounded by a non-magnetic material such as oxide is proposed. The non-magnetic grain boundary separates the magnetic crystal grains in the granular magnetic recording layer and decreases magnetic exchange interactions among the magnetic crystal grains, thereby enabling noises in the magnetization transition region to be reduced. A perpendicular magnetic recording medium having a magnetic recording layer composed of a ferromagnetic alloy containing Co and Pt, and an oxide with a volume density of 15% to 40% is disclosed in JP-A No. 178413/2003.